A number of surveillance and target acquisition systems have been developed which employ a gated image intensifier tube. By using a very narrow widely spaced gating pulse the blooming effects of strong illumination sources in the field of view can be minimized. To compensate for the loss of illumination in other areas of the field of view a very intense source of gated illumination is operated in synchronism with the intensifier tube. If the illuminator emits essentially monochromatic or invisible light selective filters can be used to improve the contrast in the image and reduce the chances of saturation.
A characteristic of the device which can be used to great advantage is the narrow and uniform depth of field at all ranges. This permits the observer to examine the solid angle of view slice by slice for objects and parts of objects without the background clutter often encountered with ordinary viewers. It does, however, have the disadvantage that the observer loses the overall picture of what is occurring in the complete solid angle at any one time. A less obvious disadvantage which can be compensated manually in the above system is that the overall brightness level must be adjusted for each range due to the square law reduction in illumination.